Fifteen years ago today, Dutch researcher Kees Moeliker stumbled across the first example of homosexual necrophilia in the mallard duck. Now, lovers of weird science around the world celebrate this discovery with Dead Duck Day.

I'll leave it to the brilliant minds at Annals of Improbable Research to lay it out for you:

On June 5, 1995, a mallard duck slammed into the window of the Natural History Museum in Rotterdam, the first big step on its journey into history. Kees Moeliker, the museum's curator, subsequently published the first scientifically recorded description of homosexual necrophilia in the mallard duck (click here for PDF). The account was later honored with an Ig Nobel Prize.

Now, every year, he reenacts this great moment in natural history by celebrating Dead Duck Day. And you can too!